The present invention relates to an endless flexible conveyor belt.
More particularly, the invention relates to an endless flexible conveyor belt of the type which is of box-shaped or trough-shaped cross-section, i.e., which has a bottom wall and side walls which extend upwardly from the same.
Still more particularly, the invention relates to such an endles flexible conveyor belt which has side walls provided with corrugations.
Conventional endless conveyor belts are, in their simplest execution, endless strips of flexible material which are trained about reversing rollers. There are many types of materials which can not be conveyed on these belts, because they drop off the lateral edges of the belt.
To avoid this problem it has been proposed to utilize an endless conveyor belt of box-shaped or trough-shaped cross-section, i.e., a belt having the usual strip-shaped supporting portion which is smooth and is trained about smooth drum-shaped reversing rollers and sidewalls which project normal or otherwise inclined to the plane of the supporting portion. This type of belt is especially advantageous for applications where material is to be transported between two or more levels, e.g., a higher level and a lower level.
However, when the conveyor belt is deflected from one level to another level, it is necessary that the sidewalls be able to accommodate themselves to the change of direction which takes place at each point of deflection, i.e., depending upon the direction of deflection the sidewalls must be able to longitudinally stretch or undergo compression. To facilitate this it has been proposed to corrugate the sidewalls transversely to their elongation, so that the resulting folds are either pulled apart (i.e., stretched) or squeezed together (i.e., compressed), depending upon the direction of deflection. It will be evident that the degree of stretching or compression is the greater the higher the sidewalls are; the reason for this is an increase in the height of the sidewalls also results in increasing spacing of the upper free edges of the sidewalls from the neutral bending zone of the belt which in the known conveyor belts lies within the bottom wall or strip of the belt.
This, in turn, dictates the deflection radius required for deflecting the belt where the belt changes direction. For example, a known conveyor belt of the type under discussion, having sidewalls of about 300 mm height, requires a deflection radius of about 750 mm to be deflected from the horizontal into the vertical. This translates into a need for deflecting drums having a diameter of 1500 mm. When this belt is deflected around these drums the sidewalls are longitudinally compressed; the limit of possible compression is evidently reached when the adjacent folds of the corrugation move into surface-to-surface abutment with one another. This is of course generally true of all corrugated sidewalls, whether high or low, which are required to continue to extend substantially normal to the bottom wall at all times, i.e., even during deflection. The use of sidewalls which are so profiled that they fold over laterally during deflection of the conveyor belt, has been proposed but is almost completely discontinued in the industry because of their susceptibility to damage and their low ability to retain conveyed materials against spilling.
Conversely, during deflection of the belt from the upper run to the lower run or vice versa a longitudinal stretching of the sidewalls takes place. The folds formed by the corrugations open up but this is of course limited to the degree of stretching achieved at the time the sidewalls have become completely flat, i.e., until the folds have been stretched flat. The degree of stretching is therefore limited by the amount of sidewall material which is "stored" in the folds. Evidently, additional material could be "stored" in this manner by increasing the depth of the corrugations, i.e., the depth of the folds in transverse direction of the belt. This, however, results in a corresponding decrease of the available load-carrying space of the belt; if one seeks to maintain that space unchanged, then the only alternative solution is to make the overall width of the belt correspondingly greater. A decrease in the load-carrying space is evidently undesired whereas an increase in belt width is often unacceptable because of space limitations at the point of use; also, belt widths are generally fixed by industrial and/or government norms.
The corrugating of sidewalls is also governed by other considerations. Thus, if the corrugated sidewall projects upwardly from the bottom wall by a distance greater than about 160 mm, it must be made specially resistant to folding-over in the lateral direction. Until now this was achieved by simply widening the corrugations in longitudinal direction of the sidewall, i.e, by making them wider in that direction than would otherwise be the case. However, this leads to deeper folds and a concomitant loss of carrying capacity. Moreover, conveyed matter tends to settle in such deep folds and, after unloading of the belt, travels along in the return run and becomes scattered during such travel.
In my prior U.S. Pat. No. 3,464,538 I have attempted to counteract the above problem by filling the sidewall folds at least partially with an elastic material to obtain improved stability and a better self-cleaning effect of the folds. However, I have found it to be a disadvantage of that construction that greater amounts of material are required to construct the belt and that the overall belt weight is increased. Moreover, the lateral sidewall stability can be economically improved only up to a sidewall height of about 200 mm in that manner.
The ability of a corrugated conveyor sidewall to undergo compression and extension in respect of the deflection radius for the belt, is largely a function of the geometry of the corrugation. The known solutions are not satisfactory, especially in the case of conveyor belts intended for large-volume conveying applications.
Also, known belts of this type exhibit markedly poor roll performance, which is defined as the ability of the sidewalls to be supported and roll on supporting rollers located beneath the return run of the conveyor. Conventionally, the free edges of the folds of the sidewalls are supported on cylindrical rollers as they travel in the return run but, because of the too great distance from one fold to the next and the too great depth of the folds, the sidewalls tend to flex in direction opposite the movement of the return run. This results from the point contact pressure transmission and leads to increasing destruction of the originally smooth contact surfaces on the sidewalls. As the damage proceeds the contact surfaces become progressively more uneven and this, in turn, leads to increasing damage to the support rollers. Ultimately this causes vibrations which are transmitted to the entire conveying installation. Short of using very expensive auxiliary equipment to counter these problems, there is nothing that can be done in the prior art to avoid them.
Another disadvantage of the prior art is that the construction principles employed in these conveyors often make it impossible to produce corrugated-sidewall conveyors for special conveying applications. Yet, the increasing use of corrugated-sidewall conveyors has opened up many new fields of applications and industry is constantly asking the belt manufacturers to provide such belts for new conveying applications. For example, it is currently being requested that corrugated-sidewall belts be furnished which have a width of 4000 mm and a sidewall height of 1000 mm; these belts are, however, required for use in situations where little vertical space is available so that the large 1200 mm-diameter reversing drums ordinarily required cannot be used. The only possible compromise is to use smaller reversing drums having a diameter of only about 400 mm. Moreover, such belts have a high inherent weight which makes it impossible to support the return run on rollers, requiring instead separate supporting belts for the return run. These, in turn, require additional vertical space for their installation.
It can be concluded, then, that the ability of the corrugated sidewalls to compress and to extend is the factor which governs the diameter of deflecting drums that can be used, the deflection radius required for deflection of the belt from one level to another, and the amount of vertical space required for installation and operation of the belt. The service life of the belt is largely dependent on the corrugation profile of the sidewalls and the ability of the corrugated sidewalls to resist deformation resulting from pressures acting upon them from various directions.